1. Field of the Invention
The present invention relates to a solid electrolytic capacitor including an anode formed of any of valve metal and an alloy mainly containing valve metal, and a dielectric layer formed by anodization of the anode. More specifically, the present invention relates to a solid electrolytic capacitor intended to reduce a leakage current.
2. Description of the Related Art
In a typical structure of a solid electrolytic capacitor an oxide layer functioning as a dielectric layer is formed in a surface of valve metal by means of anodization, a cathode layer is formed thereon, and then a lead for drawing out a cathode is further attached to the cathode layer. The valve metal refers to a group of metal having a valve action, and including aluminum, tantalum, niobium, and titanium, and the like.
However, when the dielectric layer is formed for each of the above-described solid electrolytic capacitors by anodization, crystalline oxide (defects) is formed inside the dielectric layer. Thereby, cracks are caused at grain boundaries in the dielectric layer. Such defects have small resistance, and thereby cause electric currents to flow through the defects. Accordingly, these solid electrolytic capacitors have a problem that the leakage current increases.
A possible factor for the formation of the defects is attributed to oxygen contained in the valve metal. In order to suppress the leakage current, Japanese Patent Publication No. 2001-223141 discloses nitrogen-containing metal as anode metal of a solid electrolytic capacitor, and the nitrogen-containing metal is formed of a solid solution including nitrogen, and niobium or tantalum, for example.
However, even if the nitrogen-containing metal disclosed in Japanese Patent Publication No. 2001-223141 is used as the anode metal of the solid electrolytic capacitor, the effect of reducing the leakage current is still insufficient.